The invention refers to an input circuit for a monolithically integrated semiconductor storage with field effect transistors, which circuit for intensifying the known bootstrap effect comprises a dynamic charge-up circuit.
Owing to their small size and low power consumption compared with monolithically integrated storage circuits of bipolar transistors, those of field effect transistors are widely used as main storages of modern, program-controlled data processing systems.
As an input circuit for a monolithically integrated semiconductor storage designed of field effect transistors, in the following called FET, a circuit utilizing the so-called bootstrap effect is frequently used, as known from German Offenlegungsschrift 22 43 671. Such a circuit which acts as an inverter provides, when the input level is dropping, an output level rapidly rising to the value of operating voltage VH.
FET storages are frequently controlled by digital circuits designed of bipolar transistors, because their switching speed is higher than that of field effect transistors. The so-called TTL level scheme is a typical voltage level scheme for digital circuits with bipolar transistors which is a lower signal level than the operating level of FET's. There, the one binary state, e.g. the logic "zero" is assumed to be represented by a voltage in the range of 0 to 0.8 Volt, and the other binary state, e.g. the logic "one" by a voltage in the range of 2.0 Volt up to the maximum operating voltage of, e.g., 5.5 Volt. However, the upper control level typical for FET circuits, as well as the operating voltage are much higher, e.g., as VH=8.5 Volt. This means that an MOS field effect transistor with a typical threshold voltage of 1.5 Volt which in the worst case is controlled with an upper input level of 2 Volt only conducts to a relatively low extent. A thus controlled FET has a relatively high impedance in its conductive state still. It is therefore rather slow in performing a requested charging or discharging of another circuit node, or capacitor, etc. For that reason, separate level converters are frequently used at the interfaces between bipolar and FET components.